Most conventional carpets comprise a primary backing with yarn tufts in the form of cut or uncut loops extending upwardly from the backing to form a pile surface. In the case of tufted carpets, the yarn is inserted into a primary backing by tufting needles and a pre-coat or binder applied thereto. In the case of non-tufted on bonded pile carpets, the fibers are embedded and actually held in place by the binder composition.
In both cases, the carpet construction also usually includes a secondary backing bonded to the primary backing. The secondary backing provides extra padding to the carpet, absorbs noise, adds dimensional stability and often functions as a heat insulator. The secondary backing typically either a woven fabric such as jute or a foam sheet, is laminated to the primary backing by a binder composition or by an adhesive layer applied to the tuft-lock coated primary backing.
Similar techniques are used in the preparation of continuous (rolled) as well as carpet tiles with the major difference being a higher degree of rigidity, often achieved by changes in the structure or composition of the secondary backing.
Generally these applications require a high degree of water resistance, a requirement which is usually met by the use of plastisol or addition of hot melt adhesive to the primary and/or secondary backings. However environmental and safety concerns, particularly in the industrial and institutional areas where carpet tiles containing high levels of plastisol predominate, have led to the development of stringent flame and smoke retardant standards. Moreover, the use of plastisol places a further requirement on the binder utilized in the primary coating that the binder comprise a composition onto which the plastisol will have good adhesion.
Thus, the physical properties of the binder are highly important to successful utilization as a carpet backing coating for the present invention. In this regard, there are a number of important requirements which must be met by such a coating. It must be capable of being applied to the carpet and dried using the processes and equipment conventionally employed in the carpet industry for latex coating. It must provide excellent adhesion to the pile fibers to secure them firmly to the backing both in tufted and non-tufted constructions. The coating must also have low smoke density values and high flame retardant properties and must accept a high loading with fillers such as calcium carbonate, clay, aluminum trihydrate, barite, feldspar, etc. Furthermore, the coating must maintain sufficient softness and flexibility, even with high filler loading or at low temperature, to enable the carpet, if prepared in continuous form, to be easily rolled and unrolled during installation and, in the case of carpet tiles that the tile have sufficient rigidity so as to be easily set in place. The softness and flexibility properties will then vary depending on the style of carpet but in all cases, it is important that the carpet will lie flat and not exhibit a tendencey to curl or dome.
The latex binders utilized heretofore have been lacking in at least one of these critical areas. Thus, highly filled styrene butadiene systems suffer with respect to their poor adhesion to plastisol and exhibit a high degree of smoke generation; ethylene-vinyl chloride-vinyl acetate binders do not pass the most stringent smoke generation tests while low Tg ethylene vinyl acetate systems do not have adequate strength or tuft binding properties.
It is therefore an object of the present invention to provide an economical latex binder for carpets and carpet tiles characterized by a superior balance of adhesion to plastisol, low smoke generation, high flame retardance and dry and wet tuft bind strength. Further, the latex binder must be able to accept and permanently adhere to a secondary backing such as PVC plastisol, hot melt adhesive, woven fabric, as a foam or solid film or another backing composition.